Low molecular weight hydrogenated nitrile rubber

ABSTRACT

The present invention relates to hydrogenated nitrite rubber polymers having lower molecular weights and narrower molecular weight distributions than those known in the art. The present invention is also related to shaped articles containing hydrogenated nitrile rubber polymers having lower molecular weights and narrower molecular weight distributions than those known in the art.

This application is a Continuation of co-pending Ser. No. 10/878,080filed on Jun. 28, 2004, which in turn is a continuation of Ser. No.10/167,289 filed on Jun. 10, 2002, now issued into U.S. Pat. No.6,780,939 on Aug. 24, 2004, herein incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to hydrogenated nitrite rubber polymershaving lower molecular weights and narrower molecular weightdistributions than those known in the art.

BACKGROUND OF THE INVENTION

Hydrogenated nitrile rubber (HNBR), prepared by the selectivehydrogenation of acrylonitrile-butadiene rubber (nitrile rubber; NBR, aco-polymer comprising at least one conjugated diene, at least oneunsaturated nitrile and optionally further comonomers), is a specialtyrubber which has very good heat resistance, excellent ozone and chemicalresistance, and excellent oil resistance. Coupled with the high level ofmechanical properties of the rubber (in particular the high resistanceto abrasion) it is not surprising that HNBR has found widespread use inthe automotive (seals, hoses, bearing pads) oil (stators, well headseals, valve plates), electrical (cable sheathing), mechanicalengineering (wheels, rollers) and shipbuilding (pipe seals, couplings)industries, amongst others.

Commercially available HNBR has a Mooney viscosity in the range of from55 to 105, a molecular weight in the range of from 200,000 to 500,000g/mol, a polydispersity greater than 3.0 and a residual double bond(RDB) content in the range of from 1 to 18% (by IR spectroscopy).

One limitation in processing HNBR is the relatively high MooneyViscosity. In principle, HNBR having a lower molecular weight and lowerMooney viscosity would have beoter processability. Attempts have beenmade to reduce the molecular weight of the polymer by mastication(mechanical breakdown) and by chemical means (for example, using strongacid), but such methods have the disadvantages that they result in theintroduction of functional groups (such as carboxylic acid and estergroups) into the polymer, and the altering of the microstructure of thepolymer. This results in disadvantageous changes in the properties ofthe polymer. In addition, these types of approaches, by their verynature, produce polymers having a broad molecular weight distribution. Ahydrogenated nitrile rubber having a low Mooney (<55) and improvedprocessability, but which has the same microstructure as those rubberswhich are currently available, is difficult to manufacture using currenttechnologies. The hydrogenation of NBR to produce HNBR results in anincrease in the Mooney viscosity of the raw polymer. This MooneyIncrease Ratio (MIR) is generally around 2, depending upon the polymergrade, hydrogenation level and nature of the feedstock. Furthermore,limitations associated with the production of NBR itself dictate the lowviscosity range for the HNBR feedstock. Currently, one of the lowestMooney viscosity products available is Therban® VP KA 8837 (availablefrom Bayer), which has a Mooney viscosity of 55 (ML 1+4@100° C.) and aRDB of 18%.

Karl Ziegler's discovery of the high effectiveness of certain metalsalts, in combination with main group alkylating agents, to promoteolefin polymerization under mild conditions has had a significant impacton chemical research and production to date. It was discovered early onthat some “Ziegler-type” catalysts not only promote the proposedcoordination-insertion mechanism but also effect an entirely differentchemical process, that is the mutual exchange (or metathesis) reactionof alkenes according to a scheme as shown in FIG. 1.

Acyclic diene metathesis (or ADMET) is catalyzed by a great variety oftransition metal complexes as well as non-metallic systems.Heterogeneous catalyst systems based on metal oxides; sulfides or metalsalts were originally used for the metathesis of olefins. However, thelimited stability (especially towards hetero-substituents) and the lackof selectivity resulting from the numerous active sites and sidereactions are major drawbacks of the heterogeneous systems.

Homogeneous systems have also been devised and used to effect olefinmetathesis. These systems offer significant activity and controladvantages over the heterogeneous catalyst systems. For example, certainRhodium based complexes are effective catalysts for the metathesis ofelectron-rich olefins.

The discovery that certain metal-alkylidene complexes are capable ofcatalyzing the metathesis of olefins triggered the development of a newgeneration of well-defined, highly active, single-site catalysts.Amongst these, Bis-(tricyclohexylphosphine)-benzylidene rutheniumdichloride (commonly know as Grubb's catalyst) has been widely used, dueto its remarkable insensitivity to air and moisture and high tolerancetowards various functional groups. Unlike the molybdenum-basedmetathesis catalysts, this ruthenium carbene catalyst is stable toacids, alcohols, aldehydes and quaternary amine salts and can be used ina variety of solvents (C₆H₆, CH₂Cl₂, THF, t-BuOH).

The use of transition-metal catalyzed alkene metathesis has sinceenjoyed increasing attention as a synthetic method. The most commonlyused catalysts are based on Mo, W and Ru. Research efforts have beenmainly focused on the synthesis of small molecules, but the applicationof olefin metathesis to polymer synthesis has allowed the preparation ofnew polymeric material with unprecedented properties (such as highlystereoregular poly-norbornadiene).

The utilization of olefin metathesis as a means to produce low molecularweight compounds from unsaturated elastomers has received growinginterest. The principle for the molecular weight reduction ofunsaturated polymers is shown in FIG. 2. The use of an appropriatecatalyst allows the cross-metathesis of the unsaturation of the polymerwith the co-olefin. The end result is the cleavage of the polymer chainat the unsaturation sites and the generation of polymer fragments havinglower molecular weights. In addition, another effect of this process isthe “homogenizing” of the polymer chain lengths, resulting in areduction of the polydispersity. From an application and processingstand point, a narrow molecular weight distribution of the raw polymerresults in improved physical properties of the vulcanized rubber, whilstthe lower molecular weight provides good processing behavior.

The so-called “depolymerization” of copolymers of 1,3-butadiene with avariety of co-monomers (stene, propene, divinylbenzene andethylvinylbenzene, acrylonitrile, vinyltrimethylsilane anddivinyidimethylsilane) in the presence of classical Mo and W catalystsystem has been investigated. Similarly, the degradation of a nitrilerubber using WCl₆ and SnMe₄ or PhC═CH co-catalyst was reported in 1988.However, the focus of such research was to produce only low molecularfragments, which could be characterized by conventional chemical meansand contains no teaching with respect to the preparation of lowmolecular weight nitrile rubber polymers. Furthermore, such processesare non-controlled and produce a wide range of products.

The catalytic depolymerization of 1,4-polybutadiene in the presence ofsubstituted olefins or ethylene (as chain transfer agents) in thepresence of well-defined Grubb's or Schrock's catalysts is alsopossible. The use of Molybdenum or Tungsten compounds of the generalstructural formula {M(═NR1)(OR2)2(═CHR); M=Mo, W} to produce lowmolecular weight polymers or oligomers from gelled polymers containingInternal unsaturation along the polymer backbone was claimed in U.S.Pat. No. 5,446,102. Again, however, the process disclosed isnon-controlled, and there is no teaching with respect to the preparationof low molecular weight nitrite rubber polymers.

SUMMARY OF THE INVENTION

We have now discovered that hydrogenated nitrile rubber having lowermolecular weights and narrower molecular weight distributions than thoseknown in the art can be prepared by the olefin metathesis of nitrilebutadiene rubber, followed by hydrogenation of the resultingmetathesized NBR.

Thus, the present invention is directed to a hydrogenated nitrile rubberhaving a molecular weight (MW) in the range of from 30,000 to 250,000g/mol, a Mooney viscosity (ML 1+4@100 deg. C.) in the range of from 3 to50, and a MWD (or polydispersity index) of less than 2.5.

The present invention is also directed to the use of low molecularweight hydrogenated nitrile rubber for the manufacture of a shapedarticle, such as a seal, hose, bearing pad, stator, well head seal,valve plate, cable sheathing, wheel, roller, pipe seal or footwearcomponent.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates the mutual exchange (or metathesis) reaction ofalkenes.

FIG. 2 depicts the principle for the molecular weight reduction ofunsaturated polymers.

DETAILED DESCRIPTION OF THE INVENTION

As used throughout this specification, the term “nitrile polymer” isintended to have a broad meaning and is meant to encompass a copolymerhaving repeating units derived from at least one conjugated diene, atleast one α,β-unsaturated nitrile and optionally further one or morecopolymerizable monomers.

The conjugated diene may be any known conjugated diene, preferably aC₄-C₈ conjugated diene. Preferred conjugated dienes are butadiene,isoprene, piperylene, 2,3-dimethyl butadiene and mixtures thereof. Evenmore preferred C₄-C₆ conjugated dienes are butadiene, isoprene andmixtures thereof. The most preferred C₄-C₈ conjugated diene isbutadiene.

The α,β-unsaturated nitrile may be any known α,β-unsaturated nitrile,preferably a C₂-C₅ α,β-unsaturated nitrile. Preferred C₃-C₅α,β-unsaturated nitriles are acrylonitrile, methacrylonitrile,ethacrylonitrile and mixtures thereof. The most preferred C₃-C₅α,β-unsaturated nitrile is acrylonitrile.

Preferably, the copolymer contains in the range of from 40 to 85 weightpercent of repeating units derived from one or more conjugated dienesand in the range of from 15 to 60 weight percent of repeating unitsderived from one or more unsaturated nitrites. More preferably, thecopolymer contains in the range of from 60 to 75 weight percent ofrepeating units derived from one or more conjugated dienes and in therange of from 25 to 40 weight percent of repeating units derived fromone or more unsaturated nitrites. Most preferably, the copolymercontains in the range of from 60 to 70 weight percent of repeating unitsderived from one or more conjugated dienes and in the range of from 30to 40 weight percent of repeating units derived from one or moreunsaturated nitrites.

Optionally, the copolymer may further contain repeating units derivedfrom one or more copolymerizable monomers, such as unsaturatedcarboxylic acids. Non-limiting examples of suitable unsaturatedcarboxylic acids include fumaric acid, maleic acid, acrylic acid,methacrylic acid and mixtures thereof, Repeating units derived from oneor more copolymerizable monomers will replace either the nitrite or thediene portion of the nitrile rubber and it will be apparent to theskilled in the art that the above mentioned weight percents will have tobe adjusted to result in 100 weight percent. In case of the mentionedunsaturated carboxylic acids, the nitrile rubber preferably containrepeating units derived from one or more unsaturated carboxylic acids inthe range of from 1 to 10 weight percent of the rubber, with this amountdisplacing a corresponding amount of the conjugated diolefin.

Other preferred monomers include unsaturated mono- or di-carboxylicacids or derivatives thereof (e.g., esters, amides and the like)including mixtures thereof.

The HNBR of the invention is readily available in a two step synthesis,which may take place in the same reaction set-up or different reactors.

The metathesis reaction is conducted in the presence of one or morecompounds of the general formulas I, II, III or IV;

wherein:

M is Os or Ru,

R and R′ are, independently, hydrogen or a hydrocarbon seFected from thegroup consisting of C₂-C₂₀ alkenyl, C₂-C₂₀ alkynyl, C₁-C₂₀ alkyl, aryl,C₁-C₂₀ carboxylate, C₁-C₂₀ alkoxy, C₂-C₂₀ alkenyloxy, C₁-C₂₀ alkynyloxy,aryloxy, C₂-C₂₀ alkoxycarbonyl, C₁-C₂₀ alkylthio, C1-C₂₀ alkylsulfonyland C₁-C₂₀ alkylsulfinyl,

X and X¹ are independently any anionic ligand, and

L and L¹ are independently any neutral ligand, such as phosphines,amines, thioethers or imidazolidines or any neutral carbine, optionally,L and L¹ can be linked to one another to from a bidentate neutralligand;

wherein

M¹ is Os or Ru;

R² and R³ are, independently, hydrogen or a hydrocarbon selected fromthe group consisting of C₂-C₂₀ alkenyl, C₂-C₂₀ alkynyl, C₁-C₂₀alkyl,aryl, C₁-C₂₀ carboxylate, C₁-C₂₀ alkoxy, C₂-C₂₀ alkenyloxy, C₂-C₂₀alkynyloxy, aryloxy, C₂-C₂₀ alkoxycarbonyl, C₁-C₂₀ alkylthio, C₁-C₂₀alkylsulfonyl and C₁-C₂₀ alkylsulfinyl,

X² is a anionic ligand, and

L² is a neutral π-bonded ligand, independent of whether they are mono-or polycyclic,

L³ is a ligand selected from the group consisting of phosphines,sulfonated phosphines, fluorinated phosphines, functionalized phosphinesbearing up to three aminoalkyl-, ammonumalkyl-, alkoxyalkyl-,alkoxylcarbonylalkyl-, hydrocycarbonylalkyl-, hydroxyalkyl- orketoalkyl-groups, phosphites, phosphinites, phosphonites,phosphinamines, arsines, stibenes, ethers, amines, amides, imines,sulfoxides, thioethers and pyridines,

Y— is a noncoordinating anion,

n is an integer in the range of from 0 to 5;

wherein

M² is Mo or W,

R⁴ and R⁵ are, independently, hydrogen or a hydrocarbon selected fromthe group consisting of C₂-C₂₀ alkenyl, C₂-C₂₀ alkynyl, C₁-C₂₀ alkyl,aryl, C₁-C₂₀ carboxylate, C₁-C₂₀ alkoxy, CTCZO alkenyloxy, C₂-C₂₀alkynyloxy, aryloxy, C₂-C₂₀ alkoxycarbonyl, C₁-C₂₀ alkylthio, C₁-C₂₀alkylsulfonyl and C₁-C₂₀ alkylsulfinyl,

R⁶ and R⁷ are independently selected from any unsubstituted orhalo-substituted alkyl, aryl, aralkyl groups or silicon-containinganalogs thereof,

wherein

M is Os or Ru,

R and R¹ are independently selected from the group consisting ofhydrogen, substituted or unsubstituted alkyl, and substituted orunsubstituted alkyl,

X and X¹ are independently any anionic ligand, and

L and L′ are independently any neutral ligand, such as phosphines,amines, thioethers or imidazolidines or any neutral carbine, optionally,L and L¹ can be linked to one another to from a bidentate neutralligand;

Compounds of Formula I are preferred. Compounds of Formula I wherein Land L¹ are trialkylphosphines. X and X1 are chloride ions and M isRuthenium are more preferred.

The amount of compound will depend upon the nature and catalyticactivity of the compound(s) in question. Typically, the ratio ofcompound(s) to NBR is in the range of from 0.005 to 5, preferably in therange of from 0.025 to 1 and, more preferably, in the range of from 0.1to 0.5.

The metathesis reaction is carried out in the presence of a co-olefin,which is preferably a C₂ to C₁₆ linear or branched olefin such asethylene, isobutene, styrene or 1-hexene. Where the co-olefin is aliquid (such as 1-hexene), the amount of co-olefin employed ispreferably in the range of from 1 to 200 weight %. Where the co-olefinis a gas (such as ethylene) the amount of co-olefin employed is suchthat it results in a pressure in the reaction vessel in the range offrom 1×105 Pa to 1×107 Pa, preferably in the range of from 5.2×05 Pa to4×106 Pa.

The metathesis reaction can be carried out in any suitable solvent,which does not inactivate the catalyst or otherwise interfere with thereaction. Preferred solvents include, but are not limited to,dichloromethane, benzene, toluene, tetrahydrofuran, cylcohexane and thelike. The most preferred solvent is monochlorobenzene (MCB). In certaincases the co-olefin can itself act as a solvent (for example, 1-hexene),in which case no other solvent is necessary.

The concentration of nitrile polymer (NBR) in the reaction mixture isnot critical but, should be such that the reaction is not hampered ifthe mixture is too viscous to be stirred efficiently, for example.Preferably, the concentration of NBR is in the range of from 1 to 20% byweight, more preferably in the range of from 6 to 15% by weight.

The metathesis reaction can carried out at a temperature in the range offrom 20 to 140° C.; preferably in the range of from 60 to 120° C. Thereaction time will depend upon a number of factors, including cementconcentration, amount of catalyst used and the temperature at which thereaction is performed. The metathesis is usually complete within thefirst two hours under typical conditions. The progress of the metathesisreaction may be monitored by standard analytical techniques, for exampleusing GPC or solution viscosity. Whenever referenced throughout thespecification the molecular weight distribution of the polymer wasdetermined by gel permeation chromatography (GPC) using a Waters 2690Separation Module and a Waters 410 Differential Refractometer runningWaters Millenium software version 3.05.01. Samples were dissolved intetrahydrofuran (THF) stabilized with 0.025% BHT. The columns used forthe determination were three sequential mixed-B gel columns from PolymerLabs. Reference Standards used were polystyrene standards from AmericanPolymer Standards Corp.

After the metathesis reaction, the nitrile polymer must be hydrogenatedto result in a partially or fully hydrogenated nitrile polymer (HNBR).Reduction of the product from the metathesis reaction can be effectedusing standard reduction techniques known in the art. For example,homogeneous hydrogenation catalysts known to those of skill in the art,such as Wilkinson's catalyst {(PPh₃)₃RhCl} and the like can be used.

The hydrogenation may be performed in situ i.e. in the same reactionvessel in which the metathesis step is carded out, without the need tofirst isolate the metathesized product. The hydrogenation catalyst issimply added to the vessel, which is then treated with hydrogen toproduce the HNBR.

Grubb's catalyst, in the presence of hydrogen, is converted to adihydride complex (PR₃)₂RuC₁₂H₂, which is itself an olefin hydrogenationcatalyst. Thus, in a favorable one-pot reaction, Grubb's catalyst wasused to reduce the molecular weight of NBR in the presence of co-olefin.The reaction mixture was then treated with hydrogen, converting theGrubb's complex to the dihydride species, which then hydrogenated themetathesis product to produce the HNBR of the invention. The rate ofhydrogenation was lower in this case than in the case where Wilkinson'scatalyst was used for the hydrogenation step, but it is clear that suchan approach is indeed a viable one.

Hydrogenation in this invention is preferably understood by more than50% of the residual double bonds (RDB) present in the starting nitrilepolymer being hydrogenated, preferably more than 90% of the RDB arehydrogenated, more preferably more than 95% of the RDB are hydrogenatedand most preferably more than 99% of the RDB are hydrogenated.

The low Mooney HNBR, which forms an object of the invention, can becharacterized by standard techniques known in the art. For example, themolecular weight distribution of the polymer was determined by gelpermeation chromatography (GPC) using a Waters 2690 Separation Moduleand a Waters 410 Differential Refractometer running Waters Milleniumsoftware version 3.05.01. Samples were dissolved in tetrahydrofuran(THF) stabilized with 0.025% BHT. The columns used for the determinationwere three sequential mixed-B gel columns from Polymer Labs. ReferenceStandards used were polystyrene standards from American PolymerStandards Corp.

The Mooney viscosity of the rubber was determined using ASTM test D1646.

The hydrogenated nitrile rubber of the present invention is well suitedfor the manufacture of a shaped article, such as a seal, hose, bearingpad, stator, well head seal, valve plate, cable sheathing, wheel,roller, pipe seal or footwear component.

EXAMPLES Examples 1-4

Bis(tricyclohexylphosphine)benzylidene ruthenium dichloride (Grubb'smetathesis catalyst), 1-hexene and monochlorobenzene (MCB) werepurchased from Alfa, Aldrich Chemicals, and PPG respectively and used asreceived. Perbunan was obtained from Bayer Inc.

The metathesis reactions were carried out in a Parr high-pressurereactor under the following conditions: Cement Concentration 6 or 15% byweight Co-Olefin Ethylene or 1-Hexene Co-Olefin Concentration see Table1 Agitator Speed 600 rpm Reactor Temperature see Table 1 CatalystLoading see Table 1 Solvent Monochlorobenzene Substrate statisticalButadiene-acrylonitrile- copolymer with a acrylonitrile content of 34mol % and a Mooney-Viscosity ML (1 + 4) @ 100 deg. C. of 35

The reactor was heated to desired temperature and 60 mL of amonochlorobenzene solution containing Grubb's catalyst was added to thereactor. The reactor was pressurized to the desired ethylene pressurefor Examples 1-3 or to 100 psi of Nitrogen for Example 4. Thetemperature was maintained constant for the duration of the reaction. Acooling coil connected to a temperature controller and a thermal sensorwas used to regulate the temperature. The progress of the reaction wasmonitored using solution viscosity measurements for the 6% cements. Athigher cement concentration, the reaction was assumed to be completeafter 18 hours.

The hydrogenation reactions were carried out in the same reactor as themetathesis under the following conditions: Cement solid concentration12% H2(g) pressure 1200 psi Agitator Speed 600 rpm Reactor Temperature138° C. Catalyst Loading (Wilkinson's) 0.08 phr Triphenylphosphine 1 phrSolvent Monochlorobenzene

The cement from the metathesis reaction was degassed 3 times with H2(100 psi) under full agitation. The temperature of the reactor wasraised to 130° C. and a 60 mL monochlorobenzene solution containingWilkinson's catalyst and triphenylphosphine was added to the reactor.The temperature was allowed to increase to 138° C. and maintainedconstant for the duration of the reaction. The hydrogenation reactionwas monitored by measuring the residual double bond (RDB) level atvarious intervals using IR spectroscopy.

Alternatively, the Ruthenium metathesis catalyst could be used tohydrogenate the polymer.

Example 1 Details

200 g of rubber was dissolved in 1133 g of MCB (15 wt.-% solid). Thecement was then charged to the reactor and degassed 3 times with C₂H₄(6.9×105 Pa) under full agitation.

Example 2 Details

200 g of rubber was dissolved in 1133 g of MCB (15 wt-% solid). Thecement was then charged to the reactor and degassed 3 times with C₂H₄(6.9×105 Pa) under full agitation.

Example 3 Details

75 g of rubber was dissolved in 1175 g of MCB (6 wt.-% solid). Thecement was then charged to the reactor and degassed 3 times with C₂H₄(6.9×105 Pa) under full agitation.

Example 4 Details

75 g of rubber was dissolved in 1175 g of MCB (6 wt.-% solid). Thecement was then charged to the reactor. 150 g of 1-hexene was added tothe reactor and the mixture was degassed 3 times with dry N2 under fullagitation. TABLE 1 Experimental Details Example 1 Example 2 Example 3Example 4 Cement 15% 15% 6% 6% Concentration Co-olefin C₂H₄ C₂H₄ C₂H₄1-hexene Co-olefin 500 psi 500 psi 500 psi 150 g Concentration Reactor80° C. 80° C. 80° C. 80° C. Temperature Catalyst Load 0.05 phr 0.10 phr0.25 phr 0.25 phr

For a typical product the Mn is 27 kg/mol (compared to 85 kg/mol for thestarting polymer) while the Mw is 54 kglmol (compared to 296 kg/mol forthe starting polymer). As expected, the molecular weight distributionfalls from 3.4 for the starting substrate feedstock to 2.0 for themetathesized product. This is consistent with a more homogeneous rangeof polymer chain lengths and molecular weights.

A summary of the polymer properties for selected samples is shown inTable 2. The GPC results show up to a fivefold reduction in Mw and anarrowing of the polydispersity index to a minimum of 1.90. TABLE 2Summary of Polymer Properties: Mooney Viscosity (ML 1 + 4 @ 100 MN MW MZPDI deg C.) Therban ® 98000 320000 945000 3.27 73 A3407 (Comp.)Substrate 85000 296000 939000 3.50 Experiment 1 73000 189000 441000 2.5943 Experiment 2 60000 136000 277000 2.27 28 Experiment 3 31000 5900098000 1.90 3 Experiment 4 55000 111000 1197000 2.02 31

Although the invention has been described in detail in the foregoing forthe purpose of illustration, it is to be understood that such detail issolely for that purpose and that variations can be made therein by thoseskilled in the art without departing from the spirit and scope of theinvention except as it may be limited by the claims.

1. A hydrogenated nitrite rubber comprising repeating units derived from at least one conjugated diene, at least one α,β-unsaturated nitrile and optionally further one or more copolymerizable monomers, wherein the rubber has a molecular weight (MW) in the range of from 30,000 to 250,000, a Mooney viscosity (ML 1+4 @100 deg. C.) in the range of from 3 to 50, and a MWD (or polydispersity index) of less than 2.5, wherein the hydrogenated nitrile rubber is prepared by olefin metathesis of at least one conjugated diene, at least one c,-unsaturated nitrile and optionally further one or more copolymerizable monomers in the presence of one or more compounds of the general formula I, II, III or IV and optionally the presence of a co-olefin and a solvent, wherein,

wherein: M is Os or Ru, R and R1 are, independently, hydrogen or a hydrocarbon selected from the group consisting of C₂-C₂₀ alkenyl, C₂—O₂₀ alkynyl, C₁-C₂₀ alkyl, aryl, C₁-C₂₀ carboxylate, C₁-C₂₀ alkoxy, C₂-C₂₀ alkenyloxy, C₂-C₂₀ alkynyloxy, aryloxy, C₂-C₂₀ alkoxycarbonyl, C₁-C₂₀ alkylthio, C₁-C₂₀ alkylsulfonyl and C₁-C₂₀ alkylsuffinyl, X and X1 are independently any anionic ligand, and L and L1 are independently any neutral ligand or any neutral carbine, optionally, L and L1 can be linked to one another to from a bidentate neutral ligand;

wherein M1 is Os or Ru; R2 and R3 are, independently, hydrogen or a hydrocarbon selected from the group consisting of C₂-C₂₀ alkenyl, C₂-C₂₀ alkynyl, C₁-C₂₀alkyl, aryl, C₁-C₂₀ carboxylate, C₁-C₂₀ alkoxy, C₂-C₂₀ alkenyloxy, C₂-C₂₀ alkynyloxy, aryloxy, C₂-C₂₀ alkoxycarbonyl, C₁-C₂₀ alkylthio, C₁-C₂₀ alkylsulfonyl and C₁-C₂₀ alkylsulfinyl, X2 is a anionic ligand, and L2 is a neutral π-bonded ligand, independent of whether they are mono- or polycyclic, L3 is a ligand selected from the group consisting of phosphines, sulonated phosphines, fluorinated phosphines, functionalized phosphines bearing up to three aminoalkyl-, ammonumalkyl-, alkoxyalkyl-, alkoxylcarbonylalkyl-, hydrocycarbonylalkyl-, hydroxyalkyl- or ketoalkyl-groups, phosphites, phosphinites, phosphonites, phosphinamines, arsines, stibenes, ethers, amines, amides, imines, sulfoxides, thioethers and pyridines, Y— is a non-coordinating anion, n is an integer in the range of from 0 to 5;

wherein M2 is Mo or W, R4 and R5 are, independently, hydrogen or a hydrocarbon selected from the group consisting of C₂-C₂₀ alkenyl, C₂-C₂₀ alkynyl, C₁-C₂₀ alkyl, aryl, C₁-C₂₀ carboxylate, C₁-C₂₀ alkoxy, C₂-C₂₀ alkenyloxy, C₂-C₂₀ alkynyloxy, aryloxy, C₂-C₂₀ alkoxycarbonyl, C₁-C₂₀ alkylthio, C₁-C₂₀ alkylsulfonyl and C₁-C₂₀ alkylsulfinyl, R6 and R7 are independently selected from any unsubstituted or halo-substituted alkyl, aryl, aralkyl groups or silicon-containing analogs thereof,

wherein M is Os or Ru, R and R1 are independently selected from the group consisting of hydrogen, substituted or unsubstituted alkyl, and substituted or unsubstituted alkyl, X and X1 are independently any anionic ligand, and L and L1 are independently any neutral ligand or any neutral carbine, optionally, L and L1 can be linked to one another to from a bidentate neutral ligand, and wherein the nitrile rubber is hydrogenated in situ during the metathesis reaction or wherein the nitrile rubber is subsequently hydrogenated.
 2. A hydrogenated nitrile rubber according to claim 1 wherein the molecular weight (Mw) is in the range of from 40,000 to 220,000.
 3. A hydrogenated nitrile rubber according to claim 1 wherein the polydispersity index is less than 2.3.
 4. A hydrogenated nitrile rubber according to claim 1 wherein the rubber has a Mooney viscosity (ML 1+4@100 deg. C.) of less than
 35. 5. A shaped article comprising a hydrogenated nitrile rubber according to claim
 1. 6. A shaped article according to claim 5, wherein the shaped article is a seal, a hose, a bearing pad, a stator, a well head seal, a valve plate, a cable sheathing, a wheel, a roller or a pipe seal. 